package com.baimo.support.utils;

import java.security.MessageDigest;

/**
 * 
 *<p>Description : MD5消息加密</p>
 *<p>Remark      : </p>
 * @version
 */
public class MD5Utils {
	
	/**
	 * MD5加密信息
	 * 
	 * @param message 
	 * @return 加密信息
	 * @throws Exception
	 *          异常
	 */
	public static String encrypt(String message) throws Exception {
		return encrypt(message, "MD5");
	}

	// algorithm: MD5 or SHA-1
	// return string length: 32 if algorithm = MD5, or 40 if algorithm = SHA-1
	public static String encrypt(String message, String algorithm)
			throws Exception {
		if (message == null) {
			throw new Exception("message is null.");
		}
		if (!"MD5".equals(algorithm) && !"SHA-1".equals(algorithm)) {
			throw new Exception("algorithm must be MD5 or SHA-1.");
		}
		byte[] buffer = message.getBytes();

		// The SHA algorithm results in a 20-byte digest, while MD5 is 16 bytes
		// long.
		MessageDigest md = MessageDigest.getInstance(algorithm);

		// Ensure the digest's buffer is empty. This isn't necessary the first
		// time used.
		// However, it is good practice to always empty the buffer out in case
		// you later reuse it.
		md.reset();

		// Fill the digest's buffer with data to compute a message digest from.
		md.update(buffer);

		// Generate the digest. This does any necessary padding required by the
		// algorithm.
		byte[] digest = md.digest();

		// Save or print digest bytes. Integer.toHexString() doesn't print
		// leading zeros.
		StringBuffer hexString = new StringBuffer();
		String sHexBit = null;
		for (int i = 0; i < digest.length; i++) {
			sHexBit = Integer.toHexString(0xFF & digest[i]);
			if (sHexBit.length() == 1) {
				sHexBit = "0" + sHexBit;
			}
			hexString.append(sHexBit);
		}
		return hexString.toString();
	}
	
	/**
	 * MD5的算法在RFC1321 中定义 在RFC 1321中，给出了Test suite用来检验你的实现是否正确： MD5 ("") =
	 * d41d8cd98f00b204e9800998ecf8427e MD5 ("a") =
	 * 0cc175b9c0f1b6a831c399e269772661 MD5 ("abc") =
	 * 900150983cd24fb0d6963f7d28e17f72 MD5 ("message digest") =
	 * f96b697d7cb7938d525a2f31aaf161d0 MD5 ("abcdefghijklmnopqrstuvwxyz") =
	 * c3fcd3d76192e4007dfb496cca67e13b 传入参数：一个字节数组 传出参数：字节数组的 MD5 结果字符串
	 */
	public static String getMD5(byte[] source) {
		String s = null;
		char hexDigits[] = { // 用来将字节转换成 16 进制表示的字符
		'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd',
				'e', 'f' };
		try {
			MessageDigest md = MessageDigest
					.getInstance("MD5");
			md.update(source);
			byte tmp[] = md.digest(); // MD5 的计算结果是一个 128 位的长整数，
										// 用字节表示就是 16 个字节
			char str[] = new char[16 * 2]; // 每个字节用 16 进制表示的话，使用两个字符，
											// 所以表示成 16 进制需要 32 个字符
			int k = 0; // 表示转换结果中对应的字符位置
			for (int i = 0; i < 16; i++) { // 从第一个字节开始，对 MD5 的每一个字节
											// 转换成 16 进制字符的转换
				byte byte0 = tmp[i]; // 取第 i 个字节
				str[k++] = hexDigits[byte0 >>> 4 & 0xf]; // 取字节中高 4 位的数字转换,
															// >>>
															// 为逻辑右移，将符号位一起右移
				str[k++] = hexDigits[byte0 & 0xf]; // 取字节中低 4 位的数字转换
			}
			s = new String(str); // 换后的结果转换为字符串

		} catch (Exception e) {
			e.printStackTrace();
		}
		return s;
	}

}
